40 hp Merc OB wont go WOT, only 3900 rpm???

Heinz CA.

Petty Officer 3rd Class
Joined
Sep 6, 2002
Messages
92
Just got back from fishing in Sierras(nice!), had 17' alum. boat w/ 2 stroke 40 hp Merc. out on Crowley Lake(central CA by Mammoth). Was at 7000'. Started OK, after a few starts(not ran in 2-3 months) and cruised fine. Tried to go wide open and it only hits 3900 rpm, and topped out at only 17 w/ me 170lbs and 2 buddies 180 & 220 lbs. I've had it up to approx. 5200 at 25 mph in the past with old dinged prop. I did have prop. replaced with identical(I comapred)after being rear ended(boat Ok trailer replaced too and ran boat right after accident that day and all was perfect) and could do 25 mph with me & 11 yr old 70 lbs in it). Gas is maybe 3-4 months old and I cleaned out tank real good before filling. It idled/trolled 5 mph great all day. Had to keep squeezing primer bulb when bogging to keep speed up most times. Replaced bulb, in line fuel filter and tank to gas line fitting last night, will try taking her out this weekend. Any hints?? I could see it maxing out at 17 mph due to the weight of 3 guys and gear, but I should still be able to get up to 5200 rpm, right? Gas too old? Thanks, Heinz
 

rickdb1boat

Supreme Mariner
Joined
Jan 23, 2002
Messages
11,195
Re: 40 hp Merc OB wont go WOT, only 3900 rpm???

Sounds like a combination of thin air and weight that slowed you down. You will not see 5200 RPM's with a heavy load at Higher Elevations or at any Elevation for that Matter. The more weight you put in the boat, the slower it will go and your RPM's will decrease. As for having to pump the bulb, I still believe that was due to the Motor struggling to get a proper mixture with the load and air holding it back. Try it again with a light load and see what happens!
 

Heinz CA.

Petty Officer 3rd Class
Joined
Sep 6, 2002
Messages
92
Re: 40 hp Merc OB wont go WOT, only 3900 rpm???

I'll try that this weekend on Delta, with just me and at sea level, Thanks, Heinz
 
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